The invention relates to an arrangement for the lubrication of the piston member of an injection pump for fuel or the like pressure medium.
Feeding of fuel into a cylinder of an internal combustion engine by means of an injection pump takes place under high pressure. For this reason, the clearance between the sliding surfaces of the cylinder element and the piston member of the pump is very tight, only some thousandths of millimeter, so that fuel could not essentially leak therethrough into the inner parts of the pump. Generally, the purpose of the lubrication system for the piston member of an injection pump is not only to provide lubrication of the piston but also to make said clearance more tight and, thus, to prevent for its part fuel leakages. In addition, the lubrication provides cooling, protection and purification.
In known lubrication systems, the lubrication oil is led into said clearance by making use of pressure. Due to the narrowness of the clearance, however, the oil flow is slow, even at a high feeding pressure. In addition, the lubrication oil warms up in the narrow clearance so that it exceeds desired values, about 110.degree.-115.degree. C. for mineral oils, whereby especially in a big diesel engine when heavy oil is used as fuel the warmed-up lubrication oil reacts more easily with the fuel and forms a sticky lacquer and carbon deposit, which can make it more difficult for the piston member to move in the cylinder and may even cause the feeding ducts for the lubrication oil to become entirely obstructed. It should be observed that in the context of this invention the term "big diesel engine" refers to a diesel engine that is suitable for use as a main propulsion engine or an auxiliary engine for a ship, or in diesel heating power plants, etc.